Pronombres de objeto directo
Once everybody knows what you are talking about, Spanish stops repeating the noun: —¿El libro? —Lo tengo. Seven small words do all of that work — me, te, lo, la, nos, los, las — and their usual seat is in FRONT of the verb, which is the part an English speaker has to unlearn. Los and las also cover 'you all', because plural 'you' here is ustedes.
The seven
me = me. te = you, one person you call tú. lo = him, it (masculine), or you when you are addressing one man as usted. la = her, it (feminine), or you addressing one woman as usted. nos = us. los = them (masculine or mixed) — and you all. las = them (feminine) — and you all, when everyone in the group is a woman. Three of them — la, los, las — are spelled exactly like the articles from lesson 4, so the spelling is barely anything new; what is new is where they go. The row worth underlining is the plural: plural 'you' is ustedes, so 'you all' as an object is simply los or las. Los invito a la casa. is what you say to your cousins and to your boss alike — one form covers friends and strangers both.
In front of the verb, not after it
English hangs the pronoun off the back of the verb — 'I see her'. Spanish puts it in front: La veo. Te escucho. Nos invitan. Nothing squeezes in between; the pronoun and the verb travel as one block. A question keeps that same order, it just adds the marks: ¿Lo tienes?, ¿Las compraste? A negative puts no in front of the whole block: No lo veo., No las tengo acá. If you catch yourself writing Veo la or No veo lo, that is English word order wearing Spanish words.
It has to match the noun
The pronoun copies the gender and number of the noun it is standing in for, so you have to know which noun you replaced. Compro el libro → Lo compro. Compro la fruta → La compro. Vendo los mapas → Los vendo. Escucho las canciones → Las escucho. This has nothing to do with who is speaking: the la in La compro is feminine because fruta is feminine, not because a woman is doing the buying. And remember the gender traps from lesson 5 — el mapa is masculine, so it takes lo, never la.
lo for him, and lo for a whole idea
When the object is a person the same seven words do the job, with no change at all. A man or a boy takes lo: ¿Y Pablo? Lo vi en el mercado. (vi = I saw). A woman or a girl takes la: A Camila la vi en la clase. A mixed group takes los. Say that flatly to yourself, because it is exactly where learners hesitate: lo is the direct object for a man just as much as for a thing. The word le does exist, but it has a completely different job — it points at the person something is given, said or brought TO — and that is the next lesson. Separately, lo has one use with no gender behind it at all: it stands in for an entire thought. —¿Ana trabaja mañana? —No lo sé. literally 'I don't know it', meaning 'I don't know that'. Same with Lo entiendo ('I get it') and No lo creo ('I don't believe it'). English usually drops that little word; Spanish keeps it.
The personal a disappears
When the object is a person, the noun version carries the personal a you met in lesson 10: Veo a Camila., Invito a mis amigos. Swap in the pronoun and the a leaves with the noun: La veo., Los invito. Never a la veo. The a only comes back when the noun itself comes back.
Glued onto the infinitive
With ir a + infinitive from last lesson, or querer + infinitive, the pronoun has two possible homes and both are fully correct. Either it stands in front of the conjugated verb, or it is glued onto the END of the infinitive as a single written word: Lo voy a traer. = Voy a traerlo. Te quiero ver. = Quiero verte. No space and no hyphen — traerlo, verte, invitarnos, comprarlas. You will hear both versions in the same conversation, so use whichever reaches your mouth first.
Naming the thing first, and using the pronoun anyway
Very often the noun gets moved to the front of the sentence for emphasis and the pronoun still appears in its usual seat: El pan lo compré en la tiendita. A Camila la invitamos el domingo. To an English ear that sounds like saying it twice, but it is ordinary, extremely frequent Spanish — the fronted noun announces the topic, and the pronoun keeps the grammar intact. Notice the a in front of Camila: a fronted person still takes the personal a.
